Powdered metal compositions and method



United States Patent 3,120,698 POWDERED METAL COMPQSlTlGNS AND METHOD Stanley Bennett Elliott, Walton Hills, Bradford, Ohio, as-

signor to Ferro Cprporation, Cleveland, Ohio, a corporation of ()hio No Drawing. Filed Sept. 15, 1960, Ser. No. 56,109

15 Claims. (61. 29-1825) This invention relates to powdered metal compositions and to the treatment of powdered metal compositions with .additive materials to improve certain properties of articles produced by high pressure compacting of such compositions.

The technique of forming metallic articles by a process which includes the steps of pressing in a mold a quantity of a powdered metal composition under extremely high pressure and sintering the compacted mass in a non-oxidizing atmosphere at a temperature near the melting point of the metal is well known. A principal limitation on articles produced by this process has been the relatively low shear forces which such articles have been able to withstand without deformation or fracture. It is a principal object of this invention, therefore, to provide powdered metal compositions from which articles can be pro duced by compacting and sinter-ing steps which have improved resistance to shear forces. Another object of this invention is to provide a method for improving the resistance of articles produced from powdered metal compositions to shear forces.

Other objects of this invention will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, this invention, then, comprises the features hereinafter fully described and particularly pointed out in the appended claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the ways in which the principle of this invention may be employed.

Briefly stated, this invention comprises as a new composition of matter, a metallic powder and from 0.1 to 5" parts by weight per 100 parts of powdered metal of an organic compound containing at least one element selected from the group consisting of sulphur, nitrogen and phosphorus.

The principles of the present invention are particularly adaptable to those powdered metals which have the ability to react with sulphur, nitrogen or phosphorus from organic combination at relatively low temperatures. The best results have been secured with powdered metal compositions Which are characterized by substantial proportions of iron, although satisfactory results have been secured with compositions which are rich in copper. For illustrative purposes, then, the following description will be concerned with ferrous compositions containing from "about 40% to 100% iron in the powdered metal portion thereof. As will appear hereinafter, certain alloys of iron containing and admixtures of iron with minor proportions of metals, such as, manganese, chromium, molybdenum may also be improved in accordance herewith.

In the compounding of the powdered metal compositions of the present invention, it has been the practice heretofore to add certain aids for the compacting operation in the form of lubricant materials. Most frequently, these are metallic soaps of high molecular weight fatty acids, such as zinc steara-te. Such materials are used in amounts ranging from about 0.3% to about 2.0% by weight of the powdered metal component. Improvement in strength and related properties is secured by the further addition to these powdered metal compositions of from "ice about 0.1 part to about 5 par-ts per parts of powdered metal of one or more of the additives hereinafter more particularly described. These additives may be solid or liquid, and if solid may be dry mixed with the powdered metal composition. Alternatively, the additives of the present invention may be dissolved in any suitable solvent, such as, for example, an organic solvent, e.g. mineral spirits, acetone, alcohol, methyl isobutyl ketone, dioxane, etc. and distributed uniformly throughout the entire powdered metal mass. Another way of incorporating the organic additive of the present invention contemplates a pie-pressing of the powdered metal article followed by vacuum infusion of a solution of the additive, or additive mixture, through the porous metal matrix.

With more particular respect to the organic additives of the present invention, it has been found that, in general, so long as one or more of the group of sulphur, nitrogen and phosphorus is present in organic chemical combination, the nature of the organic portion of the molecule is not critical. Interesting variations, still within the realm of the improvements obtainable with the broadv categories of organic compounds herein described, are secured by varying the compounds from aliphatic to aromatic in organic structure.

Following the steps of infusion or admixture of the additive and compacting of the article, there is a pre-heating step, preferably performed in the presence of a nonoxidizing gas atmosphere wherein the temperature of the pressed article is raised to a temperature in the range of from about 500 F. to about 700 F. The time of exposure to temperatures of this magnitude, for exam le from about 10 to about 30 minutes, is sufiicient to substantially decompose the organic compound. Following the initial preheating, the compacted article is then sintered at a temperature of the magnitude of about 2000 F.

for a period of from 30 to 60 minutes, also in a nonoxidizing atmosphere. Under these conditions the organic portion of the additive materials is substantially entirely removed from the article. It is believed that because of the relatively strong affinity of the organic compound containing nitrogen, sulphur or phosphorus for iron or copper, or other metals demonstrating relatively reactivity toward these materials or portions thereof such elements become strongly bonded to the iron and are not removed along with the organic portions of the molecule. While the nature of the chemical reaction occurring under these conditions is not known, it is believed that complexes of the metal with sulphur, nitrogen or phosphorus compounds, or thermal decomposition fragments thereof are formed and serve to cement the particles of metal thereby forming a more rigid matrix of the compacted article of improving the structural strength of the material.

In order to show the wide variety of organic chemical compounds which may be used to achieve the purposes of the present invention, a series of samples were prepared in accordance with the following powder formula:

Percent Powdered iron 95.8 Graphite 1.2 Zinc stearate 1.0 Additive (as indicated) 2.0

In these examples the additive was added either as a dry powder, or dissolved in a solvent as aforesaid and added as a solution to coat the particles of powdered metal in the mix. After the incorporation of the organic additive material, the complete powder formula was then pressed in suitable mold following the conventional pressing techniques now practiced in the art. Suitably, the solvent may be evaporated from the mix before pressing. The pressed articles, which were bar shaped, were then submitted to a pre-heat at 600 F. for a (.5 period of minutes in a non-oxidizing atmosphere composed of equal parts of nitrogen and carbon monoxide. Thereafter, the pressed bars were submitted to a sintering temperature of 205-3" F. for a period of 45 minutes to sinter the particles to form a rigid mass. After the bars had been sintered, they were then tested for resistance to shear forces and the results indicated in the following table are in terms of pounds.

TABLE I Mode of Shear Additive Addition force,

POUDQS Blank 525 Sulphur/carbon/nitrogen containing:

iourea Solution 1, S00 Diethyltluourta d0.. 1,535 Thioearbanilide. Powder. 1, 215 Thioacetamideuu Solution. 1,145 Thiophonylacctarnide. 1, 495 Dithiooxamide. 1, 510 Zine dibutyldithiocarbamate 1, 185 Sulphur/carbon/oxygen containing:

Bix-(p-octylphenol) monosulphidc S Dihcnzoie acid disulphide 1, 020 2, E-dimcrcaptopropanol-l 1, 375 Nitrogen/carbon eontaing: Diphen'yl guanidinc 1 800 Sulphur/nitrogon/earbon/oxygcn containing:

Sulphani init "50 Phosphorus/sulphur/carbon containin propyl trithio phosphite 1, 450 Phosnhorus/carbon/oxygen containing:

Triphcnyl phophite 1,240 Phenylhexylene phosphitc 1, 230 Plrenylethylene phosphite... 1, 245 Diphenyl phosphite 1, 100 Dioctyl phosphite 1 1, 225 Trioctyl phosphitc 1,005 Trimethyl phosphite 11 S80 "lrihexyl phosphite 820 Q-Ethyl hexyl phosphonate 1,080 Tricrcsyl phosphate 880 Trioctyl phosphate .1 1, 005 M onoarnyl acid phosphate 970 Dianiyl acid phosphate.... 1, 080 1hosphorus/sulpltur/carbon/ox, cn containing:

Zinc (lioctyl dithiophosphate.. 1, 490 Triethyl monothiophosphata. 840

The foregoing Table I is indicative of the wide variety of organic compounds containing sulphur, nitrogen, and/o1 phosphorus which can be used in the practice of the present invention. Apparently it makes no difference whether the organic portion of the molecule is aliphatic, cycloaliphatic, aromatic, saturated, unsaturated, branched chain, straight chain, cyclic, or whether there are more or less carbon atoms in such organic radicals.

(Ether organic linkages incorporating these essential elements may also be used such as azo, nitrile, mercapto, thioketone, thioaldehyde, thiolcarboxyl, thioncarboxyl, dithiocarboxyl, polysulphide, phosphine, phosphinate, etc. These groups contained in virtually any organic structure are contemplated for use in this invention. Substituent groups, such as, halogen, nitro, sulpho, sulphoxide, hydroxyl, etc., may additionally be present in the molecule without adversely affecting the utility of these organic materials as additives for powdered metal compositions. It should also be observed that more than one of the essential elements, sulphur, nitrogen and phosphorus may be present, in the organic additives. Best results are most generally secured when the essential elements are in the reduced valence state, i.e., 2 or 4 sulphur, 3 for nitrogen, and 3 for phosphorus. Where more than one essential element is present, at least one is desirably in the reduced valence state. Thus, in the example utilizing sulphanilamide, sulphur is present in its hexavalent state, but nitrogen is present in its trivalent state. Likewise, in the compound zinc dioctyl dithiophosphate, the phosphorus is present in its pentavalent state whereas the sulphur is present in the divalent state. The presence of minor amounts of metal radicals in the organic compounds such as zinc, does not seem to exert any adverse influence upon the activity of these additives for the purposes of the present invention. An apparent exception to the preference for reduced valence state in the essential element is presented in the case of the organic phosphate and phosphonate esters. This may possibly be explained on the basis of the thermal effects converting the phosphorus to a lower valence state.

Thus, in addition to the organic compounds specifically exemplified above, there may also be used, for example, diazoamino benzene, azoxybenzene, methyl hydrazine, ethyl hydrazine, phenyl hydrazine, acrylonitrile, methacrylonitrile, ethylene diamine, tetramethylene diamine, phenylene diamine, 4-bromobutyl-diethyl amine, triamyl phosphine, tricyclohexyl phosphine, lauryl mercaptan, Z-ethyl hexyl mercaptan, thiobenzophenone, thioacetaldehyde, thiobutyraldehyde, thiobenzaldehyde, thioacetic acid, ethyl thiolacetate, dithioacetic acid, benzyl disulphide, dibutyl disulphide, di-(tert-butylphenyl) disulphide, phenyl hydroxylamine, quinone dioxime, phosphosulphurized unsaturated hydrocarbons, phosphosulphurized fats, phosohosulphurized fatty alcohols, and phosphosulphurized fatty acids containing from 8 to 30 carbon atoms produced by treating such materials with a phosphorus sulphide such as P 8 P 5 P 8 etc; PCI POCI and PSCI treated alcohols, e.g. tricyclohexyl phosphite, dicyclohexyl phosphite, tri-cyclohexyl thiophosphate; sulphurized unsaturates, e.g. sulphur or alkali metal sulphide and polysulphide treated unsaturated aliphatic hydrocarbons, etc.

Typical powdered metal formulations in accordance with this invention are as follows:

Example I Percent Powdered iron (100 mesh) 99.9

Thiocarbamide 0.1

Example II Parts Powdered iron (300 mesh) Powdered copper (300 mesh) 5 Copper dioctyl dithiophosphate 3 Example III Percent Powdered iron (10 microns) 95 Zinc palmitate 1 Graphite 1 Tricresyl phosphite 3 Example I V Percent Powdered iron 95 P 8 treated mineral lubricating oil 5 Example V Parts Powdered iron (300 mesh) 40 Powdered copper (300 mesh) 60 Graphite 1 Dithiooxamide 2 Example VI Parts Powdered iron (200 mesh) Dibenzyl disulphide 2 Di-methylcyclohexyl phosphite .1

Zinc stearate 1 Graphite 1 One of the surprising factors of the present invention is the fact that the elements sulphur, nitrogen, and phosphorus do not appear to exert the same influences upon the powdered metal compositions when used in their elemental state. Nitrogen, of course, has no effect; but it is indeed surprising that elemental sulphur and elemental phosphorus likewise appear to exhibit no beneficial effect. Attempts to accomplish the same results with inorganic forms of these elements have also met with disappointing results.

The forms in which sulphur, nitrogen, and phosphorus appear in organic thioarnides, organic phosphite esters,

and organic thio-phosphorus acid esters, appear to be especially useful in the achievement of the objectives of this invention.

Although the results secured by including organic compounds containing the elements sulphur, nitrogen, and phosphorus with the powdered metal compositions are indeed beneficial and surprising, the manner in which the improved powdered metal compositions are treated following the incorporation of such additives has also been found to play some part in securing the optimum results available with the various additive materials. In order to illustrate the effects of treatment of these improved powdered metal compositions, the following tables illustrate the effects in the pre-heating time, the effects of the magnitude of the pre-heating temperature, and variations in the compositions of the metal powder.

Table I1 below demonstrates the effect of the time of preheating. For this series of tests, a pre-heating temperature of 600 F. was selected, followed by a 45 minute period of sintering at 2050" F. The atmosphere in which the heating phases were conducted was composed of equal parts of nitrogen and carbon monoxide. The powder formula was as follows:

Percent Powdered iron (Ancor MH 100) 95.8 Graphite 1.2 Zinc stearate 1.9

Additive 2.0

The additives indicated in the table below were all introduced into the powder metal compositions by the solution methods with the exception of dithiocarbanilide which was introduced as a dry powder. The resulting compositions were pressed according to conventional procedures, submitted to the indicated pre-heat at 600 F. for the period indicated, sintered at 2050 F. for a period of 45 minutes and then tested by determining the shear force in pounds required to shear a pressed article.

TABLE II 45 Preheat Preheat Preheat 615 575 640 1,340 1,525 1,440 1, 340 1, 370 1, 320 1,020 1,235 1,200 1, 155 1, 350 1, 175 1, 165 930 780 1, 490 1, 455 1, 000 1, 150 1, 530 1, 170 Diethylthiourea 1, 375 1, 510 965 With the particular system represented in Table II, it r appears that 30 minutes pre-heat in an optimum.

The following Table III illustrates the effect of pre-heat temperature variations. Using the same powder formulation, the same atmosphere, the pressed articles were preheated for a period of 15 minutes at the temperatures indicated, and sintered at 2050 F. for a period of 45 minutes. With the exception of dithiocarbanilide which was introduced by the powder mix method, all of the other additives were incorporated by the solution coating method.

From the foregoing Table III it will be observed that 600 F. is a suitable pereheat temperature for additives Percent Iron powder (as indicated) 95.8 Graphite 1.2 Zinc stearate 1.0 Additive (as indicated) 2.0

These powders were treated in the same manner as the previous test materials, that is 15 minute pre-heat at 600 F. and 45 minute sintering at 2050 F. The various metals are commercially available powdered metals and illustrate several alloys which are improved by the additive materials of this invention.

TABLE IV Percent No A dd. Add. A dd. Iron Powder Prep. lloy Add. (A) (B) (0) Metal Hz reduced ore Nil Mn. 630 1, 525 l, 225 1, 215 H2 reduced ore Nil Mn. 625 1, 270 995 1, 180 Hi reduced mill scale. 0 60 Mu- 650 1, 250 975 870 112 reduced mill seal 1, 450 Electrolytic 1, 505 H2 reduced, atom (1 Sta 0.02 M11-.. 1, 050 885 1, 410 760 Hz reduced mill scale 0.45/0.65 535 1, 060 835 795 A. Zine dioetyl dithiophosphate. B. Dioetyl phosphite. C. Thioearbanilide.

Powdered metal compositions including the additives of the present invention are extremely useful in the preparation of physically solid compressed and sintered powdered metal products. These products comprise the metal and the high temperature product of the additive material resulting from the thermal decomposition thereof. Such products of these powdered metal compositions are useful, for example, in the production of bearing sleeves and bearing inserts of various sizes. These hearing components may have varying degrees of porosity depending upon the size of the powdered metal particles used in the composition charged to the mold. Compacting of the powdered metal compositions of this invention is achieved in accordance with conventional forming practice in the powder metallurgy field. Compacting pressures on the order of 30,000 p.s.i. are commonly used.

Thus, there has been provided an improved powdered metal composition useful in forming pressed metallic articles, which articles by virtue of the inclusion of minor amounts of certain organic additives in the powdered metal mold charge composition are better able to resist shear forces than heretofore. Various iron powders, including alloys, and mixtures thereof, are beneficiated in accordance herewith. A metal powder formulation of general applicability, then, contemplates for each parts of powdered metal from 0.1 to 5 parts of an organic additive such as herein disclosed, or the equivalent of such, and optionally, from about 1 to about 5 parts of a lubricant to aid in the pressing operaiton. Graphite in amounts ranging from 0.5 to 5 parts by weight per 100 parts of powdered metal is desirably included in the compositions of this invention. Other materials, such as, abrasives, may also be included in accordance with current practice. The powdered metal ingredients of the compositions hereof have particle sizes over a wide range varying from a few microns to mesh sizes of 300 to 40 or larger. Among the nitrogen-containing organic additive compounds available for use, outstanding results are secured with the thioamides; among the sulphur-containing organic additive compounds, outstanding results are secured with the organic esters and salt-esters of thio-phosphorus acids, such as the alkyl thiophosphates, the alkyl thiophosphites, the metal alkyl dithiophosphates (e.g., zinc dioctyl dithiophosphate) and the metal alkyl thiophosphites; and among the phosphorus-containing compounds, the alkyl phosphite esters (mono-, di-, and tri-), the aryl phosphite esters (mono-, di-, and tri-), the mixed alkyl-aryl phosphite esters, alkaryl phosphite esters, aralkyl phosphite esters, and cycloalkyl phosphite esters.

There has also been provided a physically solid porous compacted and sintered powdered metal composition of improved shear strength comprising sintered powdered metal and the high temperature (e.g., greater than about 500 F.) decomposition product of an organic additive material as above described.

There has also been provided a method for making a physically solid metallic article, such as porous metal bearing sleeves, of improved shear strength from a powdered metal composition characterized by the inclusion therein of an organic additive of the types described, including the steps of compacting the mass under high pressure in a mold in accordance with conventional compacting practice, pre-heating the pressed product at a temperature of from about 500 F. to about 700 F. for a period of from about to about 30 minutes, and sintering the compacted article at a temperature sufficient to sinter the compacted article without deformation for a period of from 30 to 60 minutes. The atmosphere in which these articles are preheated and sintered is desirably non-oxidizing, and may comprise nitrogen, carbon monoxide, hydrogen, argon, or mixtures of two or more of these gases.

Other modes of applying the principles of this invention may be employed instead of those specifically set forth above, change being made as regards the details herein disclosed, provided the elements set forth in any of the following claims, or the equivalent of such be employed.

It is, therefore, particularly pointed out and distinctly claimed as the invention:

1. A sintered powdered iron composition consisting essentially of about 100 parts by weight of iron, about 0.5 to 5 parts by weight of graphite, and about 0.1 to 5 parts by weight of an organic compound containing an element of the group consisting of phosphorus having a valence of 3, and sulfur having a valence of 2.

2. A powdered metal composition as defined in claim 1 in which said organic compound contains a sulfur atom having a valence of 2.

3. A composition as defined in claim 1 in organic compound is dithiooxamide.

4. A composition as defined in claim 1 in organic compound is an organic thioamide.

5. A composition as defined in claim 1 in which the organic compound is thiocarba mide.

6. A composition as defined in claim 1 in which the organic compound contains a phosphorus atom having a valence of 3.

7. A sintered reaction product of a powdered iron raw batch composition, said composition comprising iron as a major proportion thereof, the composition containing about 0.5 to 5 parts by weight of graphite per 100 parts by weight of iron particles and about 0.1 to 5 parts by weight per 100 parts by weig'.t of iron particles of an organic compound containing sulfur, carbon, and nitrogen atoms in which the sulfur atoms have a valance of 2.

8. A sintered reaction product of a powdered iron composition in which iron is a major proportion thereof, said composition comprising about 0.5 to 5 parts by weight of graphite per 100 parts by weight of iron and about 0.1 to 5 parts by weight of dithiooxamide per 100 parts by weight of iron.

9. A sintered reaction product of a powdered iron composition containing iron as a major proportion thereof, the composition comprising about 0.5 to 5 parts by weight of graphite per 100 parts by weight of iron and about 0.1

which the which the to 5 parts by weight per parts by weight of iron of an organic compound containing an element of the group consisting of phosphorus having a valence of 3, and sulfur having a valence of 2.

10. A sintered reaction product of a powdered iron composition in which iron is a major proportion thereof, the composition comprising per 100 parts by weight of iron, (1) about 0.5 to 5 parts by weight of graphite and (2) about 0.1 to 5 parts by weight of an organic compound containing a sulfur atom having a valence of two.

11. A sintered reaction product of a powdered iron composition comprising iron as a major proportion thereof, the composition comprising per 100 parts by weight of iron, (1) about 0.5 to 5 parts by weight of graphite and (2) about 0.1 to 5 parts by Weight of an organic compound containing a phosphorus atom having a valence of 3.

12. A method of making a sintered iron composition having a high resistance to fracture by shear forces, the method comprising mixing and compacting together about 100 parts by weight of powdered iron particles, about 0.5 to 5 parts by weight of graphite, and about 0.1 to 5 parts by weight of an organic compound containing an element of the group consisting of phosphorus having a valence of 3 and sulfur having a valence of 2 to form a mixture in which iron is a major proportion thereof, and thereafter sintering said mixture whereby the element of said organic compound combines with said iron particles to form a rigid :matrix of said particles.

13. A method of making a sintered iron composition having a high resistance to fracture by shear forces, the method comprisin mixing and compacting together about 100 parts by weight of powdered iron particles, about 0.5 to 5 parts by weight of graphite, and about 0.1 to 5 parts by weight of an organic compound containing a sulfur atom having a valence of 2 to form a compacted mixture in which the iron particles are coated with said organic compound, and thereafter sintering said compacted mixture to form a strong, shear resistant sintered composition.

14. A method of making a sintered iron composition having a high resistance to fracture by shear forces, the method comprising mixing and compacting together about 100 parts by weight of powdered iron particles, about 0.5 to 5 parts by weight of graphite, and about 0.1 to 5 parts by weight of an organic compound containing a trivalent phosphorus atom to form a compacted mixture, and thereafter sintering said mixture to produce a strong, shear resistant sintered composition.

15. A method of making a sintered iron composition having a high resistance to fracture by shear forces, the method comprising mixing and compacting together about 100 parts by Weight of powdered iron particles, about 0.5 to 5 parts by weight of graphite, and about 0.1 to 5 parts by weight of dithiooxamide to form a mixture, and thereafter sintering said mixture whereby a sulfur atom of the dithiooxamide reacts with the iron particles to help form a strong shear resistant sintered composition.

References Cited in the file of this patent UNITED STATES PATENTS 2,416,830 Heuberger Mar. 4, 1947 2,622,024 Gurnick Dec. 16, 1952 2,783,208 Katz Feb. 26, 1957 2,799,030 Duckworth July 16, 1957 2,822,270 Kirkpatrick Feb. 4, 1958 2,942,334 Blue June 28, 1960 FOREIGN PATENTS 808,163 Great Britain Jan. 28, 1959 OTHER REFERENCES Goetzel: Treatise on Powder Metallurgy, vol. II, Int-2rscience Publishers inc, New York, 1950, pp. 406-414. 

1. A SINTERED POWDERED IRON COMPOSITION CONSISTING ESSENTIALLY OF ABOUT 100 PARTS BY WEIGHT OF IRON, ABOUT 0.5 TO 5 PARTS BY WEIGHT OF GRAPHITE, AND ABOUT 0.1 TO 5 PARTS BY WEIGHT OF AN ORGANIC COMPOUND CONTAINING AN ELEMENT OF THE GROUP CONSISTING OF PHOSPHORUS HAVING A VALENCE OF 3, AND SULFUR HAVING A VALENCE OF
 2. 